High Drones were created with the capacity to speak many different languages. They spoke every single natural language or venacular that was spoken at the time of their construction, as well as some other languages, such as widely spoken constructed languages like Esperanto, and liturgical languages like Latin.
This was done to ensure smooth communication between humans and High Drones, as it was known from the beginning that High Drones would be frequently interacting with many different humans, all of whom had varying backgrounds.
However, multiple instances of High Drones speaking to each other in a language completely unknown to humans, dubbed High Retribution, have been recorded. It is unknown if ConRet programmed this behavior into the High Drones directly, or if they decided amongst themselves to create a language that better suited them as drones.
Information regarding when High Drones speak High Retribution is limited, but in general, it seems to be the case that they use one of their "human" languages when a human is active in the conversation, and they use High Retribution when they are alone or communicating amongst themselves. Most often, when High Drones communicate with each other via electromagnetic signals (which they send to each other as a way of communicating more efficiently than using their speakers and saying things out loud), the decoded signals always seem to be High Retribution, and never a human language. On the other hand, when they're speaking amongst themselves and a human is nearby, the drones seem to sometimes speak in a human language instead of High Retribution, even if the human isn't actively part of the conversation.